BUENOS AIRES, Argentina (CNN) -- Argentine first lady Cristina Fernandez de Kirchner declared victory Sunday night as election returns showed her leading all rivals in her bid to succeed her husband and become the country's first female president.

Cristina Fernandez de Kirchner shows the envelope before casting her vote at a polling station.

Fernandez de Kirchner called her victory "a triumph for all Argentines" and thanked supporters for entrusting her with the "major responsibility" of the presidency.

She also thanked her husband, center-left President Nestor Kirchner, who is expected to switch roles and become the leading adviser to his wife once she takes office.

Fernandez de Kirchner has been a top adviser to her husband during his four years in office and serves in the country's Senate. During the campaign, she promised to continue his economic policies, which she credited with reviving the country's economy after the country's 2001-2002 financial meltdown.

With just over two-thirds of polling places reporting, Fernandez had about 43 percent of the vote, compared with 23 percent for former lawmaker Elisa Carrio and 18 percent for former Economy Minister Roberto Lavagna, The Associated Press reported. Eleven others split the rest.

Six independent television networks, a private radio station and an opposition newspaper reported their exit polling indicated Fernandez has easily won a first-round victory.

But no opposition candidates conceded defeat, and Carrio spokesman Matias Mendez said seven parties had filed a complaint alleging that ballots were missing or stolen in Buenos Aires province, the country's most populous.

Electoral officials denied any irregularities, but a judge extended voting by an hour in the capital after many of Argentina's 12,700 polling stations opened late. A representative of the ruling party was arrested on suspicion of trying to vote twice.

The Kirchners have drawn comparisons to former U.S. President Bill Clinton and his wife, Sen. Hillary Clinton, now the Democratic presidential front-runner in the 2008 U.S. elections.

The next president, who begins a four-year term on December 10, faces challenges including high inflation, an energy shortage and rampant crime in a country that a century ago ranked among the world's 10 richest.

Don't Miss

Fernandez de Kirchner, 54, refused to debate and spent much of the campaign abroad in photo-ops with world leaders. Her chic European dresses and designer bags also drew comparisons with "Evita" Peron.

Fernandez de Kirchner will be the first woman elected to the Casa Rosada, though Argentina has been led by a woman once before. Isabel Peron, the wife of longtime leader Juan Peron, took office after her husband's 1974 death and ruled until she was overthrown in 1976.

Fernandez de Kirchner, who built her own independent career as her husband rose to power, has rejected comparisons to both Clinton and Evita.

She told the crowd of reporters that voting was especially joyful for her because she grew up under the 1976-83 dictatorship, according to a report from The Associated Press.

"I'm part of a generation that grew up in a country in which nobody could say anything, so we value this in a very special way," she said.

Voters were also filling dozens of House and Senate seats and nine governorships. Exit polls indicated Vice President Daniel Scioli won the governorship of Buenos Aires province, the country's second most powerful post.

Argentina's 27.1 million registered voters are required by law to cast ballots. E-mail to a friend

Journalist Brian Byrnes contributed to this report

Copyright 2007 CNN. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed. Associated Press contributed to this report.